Mechanical Properties of Niobium Alloyed Gray Iron

Abstract: The influence of adding an amount of 0.1% and 0.3% niobium to the gray iron alloy used for brake discs, these disc materials are called disc 16 respective 17, have been investigated at RT (room temperature). That is together with two other alloys, the reference disc which contains 0.32% molybdenum but lacks niobium and another one with neither niobium nor molybdenum in it, this is called disc material 15. Focus in this thesis work is on the mechanical properties of the studied materials and for this purpose the low cycle fatigue (LCF) properties of the mentioned alloys are investigated. The strain controlled LCF were done at strain amplitudes varying from 0.05 to 0.43%. According to the results, all the materials become survivors when the applied strain was 0.05%. For the other applied strain ranges the reference disc material shows the shortest life-span, while it is difficult to distinguish the other three materials. However, on average material 16 and 17 show a slightly better performance compared to material 15. This means that niobium can be used to replace molybdenum in this application. However, an obvious difference between disc material 16 and 17 cannot be observed when material disc 16 showed to be the superior at some applied strains and material disc 17 at the others. For this reason, it is more profitable to replace the 0.32% molybdenum with 0.1% niobium. The results also show that if the loading is mainly in the elastic region the life increases dramatically. It is also obvious that the static properties of gray iron increases with increasing niobium content and the fracture stress increases with about 30 MPa when the niobium contents go from 0.1% to 0.3%.